Photoelectric operated diaphragm setting means for cameras



Sept. 9, 1969 p. F'AHLENBERG PHOTOELECTRIC OPERATED DIAPHRAGM SETTING MEANS FOR CAMERAS Filed NOV. 25, 1965 2 Sheets-Sheet l Sept. 9, 1969 P. FAHLENBERG 3,466,447

PHOTOELEGTRIC OPERATED DIAPHRAGM SETTING MEANS FOR CAMERAS Filed Nov. 25. 1966 2 Sheets-Sheet a United States Patent Int. Cl. Htllj 39/12 US. Cl. 250-210 8 Claims ABSTRACT OF THE DISCLOSURE Disclosed is an electrically controlled, mechanically operated diaphragm especially useful in photographic cameras. The electronic portion comprises a photo resistor to which scene light is directed. In series with the photoresistor is a diode having a compensating logarithmic characteristic curve, whereby the combination of photo resistor and diode has a linear characteristic curve. The photo resistor and diode comprise one branch of a battery powered bridge circuit while the other branch comprises the resistance element of the potentiometer which proferably has a linear characteristic curve. Cooperating with the resistance element of the potentiometer is a slide element. One of the two elements is coupled to a rotatable diaphragm leaf positioning ring which is spring biased to a limit position in which the diaphragm aperture is generally either fully open or fully closed. The ring has circumferentially positioned detent notches for receiving a detent which is operated electromagnetically and by a spring. The other of the two elements (resistance element and slide element) can be coupled to a movable exposure time setting structure. The electromagnet coil is part of an emitter coupled Schmitt trigger circuit in combination with the bridge circuit. The operation of the trigger circuit is such that under normal operative conditions, when the potentiometer slide is at the balance voltage of the bridge circuit, the detent becomes seated in a detent receiving notch and prevents further rotation of the leaf positioning ring. Mechanical structures are provided for operating the diaphragm leaf positioning ring when the camera trip mechanism is actuated, and for releasing the detent under certain conditions. An auxiliary mechanism is provided for operating the diaphragm without tripping the shutter.

This invention relates to optical apparatus having a diaphragm with electronic means for controlling the setting of the diaphragm aperture, said means comprising at least one photo resistor to which scene light is directed and which governs the settting.

Scene light reaching the photo resistor can vary over a wide range, for example, from 1.2:50,000 foot candles, the maximum value being about 40,000 times the minimum value. Depending on the conduction characteristics of the photo resistor, this can result in the ratio of minimum electrical current to maximum electrical current through the resistor to fluctuate from as little as 1:20,000' to as much as 1:70,000. This non-linear fluctuation must be counteracted. Where the photo resistor is in one branch of a bridge circuit and the resistance element of a potentiometer is in another branch of the bridge circuit, such counteraction can be obtained by employing a resistance element that has a logarithmic voltage drop over a wide range. However, such a resistance element generally can be made only at considerable expense and is subject to extreme inaccuracies.

An object of this invention is to provide a generally improved and more satisfactory means for setting the diaphragm aperture.

3,466,447 Patented Sept. 9, 1969 Another object of this invention is to provide an electronic circuit for controlling the setting of the diaphragm aperture, which circuit has at least one photo resistor that has a non-linear characteristic curve, which circuit automatically compensates for fluctuations in the maximum to minimum current values of the photo resistor without the necessity of a logarithmic type potentiometer.

These and other desirable objects may be attained in the manner disclosed as an illustrative embodiment of the invention in the following description and in the accompanying drawings forming a part hereof, in which:

FIG. 1 is a longitudinal section through a preferred specific embodiment of a photographic camera of this invention, in which view electrical components and wiring are diagrammatically shown; and

FIG. 2 is a plan view of the photographic camera involved in FIG. 1.

The photographic camera illustrated in FIG. 2 comprises a housing 10 with a front wall in which is mounted an objective shutter 12. Within the housing 10 is a film feed and shutter cocking mechanism (not shown) which is actuated by rotation of an operating knob 14. The cocked shutter 12 is released by a trip lever 16 (see FIG. 1) which is in operative association with a catch member of the shutter blade driving mechanism (not shown). A movable camera release or trip rod 18 carries a drive pin 18a to operate the trip lever 16. The trip rod 18 has a collar 18b which normally is pressed against the upper wall of the camera by a compression spring 20. A projection 180 on the trip rod 18 is slidably disposed in a generally straight or rectilinear guideway 10a in the camera housing 10 to prevent turning of the trip rod on its longitudinal axis. A press button 18d on the upper end of the trip rod projects outwardly from the camera housing 10 and is used to operate the rod.

In addition to the shutter the housing of the objective shutter 12 contains a diaphragm. The diaphragm comprises a number of diaphragm blades or leaves 22, only one of which is illustrated in FIG. 1. Each leaf is pivotally -mounted on a pivot pin 22a and carries a control pin 22b slidably disposed in a control or guide slot 24b in a diaphragm control or aperture setting ring 24 rotatably mounted around the objective aperture. The guide slot 24b for the most part is oriented on a line of decreasing radius relative to the optical axis or center of the objective aperture. The setting ring 24 has a drive pin 24a and a radially outwardly extending arm 240 secured to the slide member 26 of a potentiometer P. When the diaphragm aperture setting ring 24 is made out of electrically conductive material, preferably there is insulation or dielectric material separating the arm 24c and the slide member 26. In addition to slidably engaging the resistance element of the potentiometer P, the slide member 26 also slidably engages a bus 27 stationarily mounted on insulation secured to the camera housing 10. The drive pin 24a of the setting ring 24 is slidably engaged by the bifurcated drive arm 28a of a double-armed transfer lever 28 rotatably mounted on a stationary or fixed pin member 10b of the camera housing 10. The other or return arm 28b of the transfer lever 28, because of a drive spring 30 in combination with the lever, normally bears against a lateral projection 32a of a flat slider or second action bar 32. This bar is positioned for vertical movement under the control of stationary pin members 1012 and of the camera housing 10, which pin members are disposed in guide slots 32b and 32c in the second action bar 32. The second action bar 32 is urged upwardly by a compression spring 34 associated therewith.

Another flat slider 36, a first action bar, is also provided. The pin members 10b and 100 of the camera housing 10 are also disposed in slots 36b and 36c in the first action bar 36. The slots 36b and 360 are generally longitudinally alined, but in the region of the bottom ends thereof they curve toward the longitudinal edge of the first action bar, which edge in the embodiment shown is the one facing the optical axis. A tension spring 38 urges the first action bar 36 upwardly so that a laterally projecting flange 36a of the first action bar bears against the collar 18b of the trip rod 18. The first action bar 36 has a lateral projection with a longitudinal extension 36d for operating the switch arm of a normally open switch S. When the switch arm is of the construction depicted in FIG. 1, at least the longitudinal extension 36d and preferably the entire first action bar 36 is made of electrically nonconductive material. The lateral projection of the first action bar 36 in the embodiment shown also has an arm or lateral extension 36c which projects outwardly through an opening in the side wall of the camera housing and provides outside of the camera housing It a finger tab.

The electronic arrangement for the automatic setting of the diaphragm aperture comprises an electromagnet M, the winding and core of which are held by a support plate 40 fastened to the camera housing 10. The electromagnet M has an armature 42 pivotally mounted on a pivot pin member 42a of the support plate 40. A spring 44 biases the armature 42 against the core of the electromagnet, in the clockwise direction in the camera shown in FIG. 1. The pivotal end 42b of the armature 42 is a catch hook or detent which is seatable in a series of detent notches 24d at the periphery of the diaphragm control ring 24. Secured to the armature 42 is one end of a leaf spring 46, the other end of which bears against a thrust arm 48a of a double-armed tensioning lever 48 pivotally mounted on a pivot pin member 10d of the camera housing 10. The other arm 48b, a follower arm, of the tensioning lever 48 coacts with the above described longitudinal edge of the first action bar 36. In combination with the tensioning lever 48 is a follower spring 50 which urges the follower arm 48b of the tensioning lever 48 toward said longitudinal edge of the first action bar 36, which is in the counterclockwise direction in FIG. 1.

The electrical components involved in the electronic arrangement illustrated in FIG. 1 comprise a battery B in series with the arm of the switch S. One output terminal of the battery is connected to one end of a bridge circuit while the contact of the switch S is connected to the other end of the bridge circuit. The bridge circuit comprises in one branch in series a photo resistor R, for example, a cadmium sulfide resistor, to which scene light from the scene to be photographed is directed, and a Zener diode Z. The other branch of the bridge circuit comprises the resistance element of the potentiometer P and in series therewith adjustable as well as temperature sensitive resistors R1 and R2. The resistance element of the potentiometer P has a linear voltage drop from one end to the other at a constant current flow therethrough. The electrical arrangement also comprises an emitter coupled Schmitt trigger circuit in which are first and second NPN transistors T1 and T2, and a collector resistor R3 for the first transistor T1. The components of the electrical arrangement are connected together as depicted in FIG. 1.

The resistance element of the potentiometer P is not stationarily mounted, but is coupled for movement with an exposure time setter 52, the structure of which in this embodiment is conventional and, therefore, only partially shown, to enable the exposure period or extent in time of the exposure to be taken into account. In the embodiment shown, the resistance element of the potentiometer P is secured to electrically insulated projections 52a and 52b of the exposure time setter 52. In other Specific em'bodiments of this invention the resistance element of the potentiometer P is coupled to the arm 240 of the diaphragm aperture setting ring 24 and the slide member 26 of the potentiometer is coupled to the exposure time setter 52.

In the embodiment shown, an iris diaphragm 54 is positioned behind the scene light window for the photo resistor R with the setting member of this diaphragm being coupled to a setting knob 56 by conventional structure diagrammatically depicted. The setting knob 56 as shown in FIG. 2 is in association with a film sensitivity or film speed scale 58.

The electromechanical structure for operating the diaphragm of the camera of FIGS. 1 and 2 functions as follows.

After the operating knob 14 has been turned so as to operate the film feed and shutter cocking mechanism, the exposure time setting ring 52 is turned to the desired setting. This causes the resistance element of the potentiometer P to be placed in a specific position. The film speed knob 56 is turned to a desired setting, whereby passage of scene light to the photoresistor R is correspondingly adjusted. The diaphragm leaves 22 in the embodiment shown are normally already at limit positions corresponding to a full diaphragm aperture. In other specific embodiments, however, the limit positions can correspond to a fully closed diaphragm aperture.

For making an exposure, the camera trip button 18d is depressed, whereby the trip rod 18 is thrust downwardly. As it moves downwardly, its collar 18b bearing against the lateral flange 32a of the first action bar 36 shifts the first action rod downwardly. During this downward movement of the first action bar 36, a transverse movement, which is to the right in FIG. 1, is imparted to the first action bar 36 by the transversely oriented portions of the slots 36b and 36c, whereby the switch arm actuator extension 36d closes the switch S. The voltage of the battery B is thereby applied to the bridge circuit and initial current flows through the electronic circuitry under the control of the photo resistor R. Under these conditions the second transistor T2 conducts current while the first transistor T1 is blocked or cut off so that it conducts substantially no current. As a result, the electromagnet M is energized and the pivotal end of the armature 42 is held against the armature core as illustrated in FIG. 1.

As the first action bar 36 continues its transverse or oblique movement, the aforementioned longitudinal edge thereof engages the follower arm 48]) of the tensioning lever 48 and turns the latter slightly, in the clockwise direction in FIG. 1, so that the thrust arm 48a applies a selected amount of pre-tensioning to the spring 46. This tensioning is not enough to overcome the counter force of the spring 44 plus the magnetic attraction of the electromagnet M.

After these preliminary actions and while the camera trip rod 18 is still moving downwardly, the lateral flange 36a of the first action bar 36 engages the upper end of the second action bar 32 and pushes it downwardly as well. The lateral projection 32a moves downwardly, whereby, because of the drive spring 30, the return arm 28b of the transfer lever 28 follows the lateral projection 32a and the drive arm 28a pivots in the direction, the clockwise direction in FIG. 1, that the diaphragm setting ring 24 must be rotated to move the diaphragm leaves 22 toward an aperture constricting position. As a result, the diaphragm leaves 22 are moved from the fully open position toward a position in which they define a diaphragm aperture with a smaller area. The diaphragm setting ring 24 as it runs down or rotates carries along with it the slide member 26 of the potentiometer P. As the slider 26 slides along the resistance element of the potentiometer P, it reaches at a certain position an electrical potential which is sufiicient to establish the threshold voltage between the emitter and the base of the first transistor T1. This transistor becomes conductive and sufiicient current flows through the collector resistor R3 that the voltage drop across it is effective to cut off or block the second transistor T2. The electromagnet M thereby becomes deenergized. This releases the armature 42 and the detent or catch hook 42b under the action of the pre-tensioned leaf spring 46 is pivoted toward the periphery of the diaphragm control ring 24 and drops into a detent notch 24d at the periphery. The run down movement or rotation of the diaphragm setting ring is thereby arrested and the aperture constricting movements of the diaphragm leaves 22 are stopped so that they define an aperture area based on the pre-selected exposure time and film speed factors and on the scene light factor as automatically determined by the photo resistor R.

Toward the end of the downward travels of the camera trip rod 18 and of the first action bar 36 and second action bar 32, the trip bar trip pin 18a strikes the shutter trip lever 16, whereby, after or at the same time as the diaphragm leaves reach the arrested position, the shutter is tripped and the photograph taken.

After the photograph has been taken and the camera trip rod 18 is released, it and the first action bar 36 are returned by their return springs 20 and 38 to their starting positions illustrated in FIG. 1. As they travel upwardly the second action bar 32, urged by its return spring 34 toward its starting position, also travels upwardly, but only until its lateral projection 32a bears against the return arm 28b of the transfer lever 28, the drive arm 28a of which is held by the still arrested diaphragm setting ring 24. It is only after the follower arm 48b of the tensioning lever 48 has been released as a result of the leftward oblique movement of the first action rod 68 that the tensioning lever by virtue of its return spring 50 is pivoted in the counterclockwise direction to its starting position, whereby the tensioning effect of the tensioning lever 48 on the leaf spring 46 and thus on the armature 42 is removed. Because of the return spring 44 the detent end 42b of the armature 52 is retracted from the detent notch 24d. Because of the return spring 34 acting on the second action bar 32, the second action bar now continues its upward travel toward its starting position and its lateral projection 32a pivots the return arm 28b in the direction, the counterclockwise direction in FIG. 1, in which the transfer lever 28 and diaphragm setting ring 24 are returned to their starting rest and limit positions illustrated in FIG. 1.

If, before taking a photograph of a scene, the operator wishes to ascertain the diaphragm aperture that will be set up when the photograph of that scene is taken, instead of depressing the camera trip button 18d and thus the camera trip rod 18, he merely presses downwardly on the finger tab of the lateral projection 36c of the first action bar 36 to move the first action bar downwardly and through its flange 36a the second action bar 32. The movements which then ensue are the same as just described, but with the sole difference that the camera trip rod 18 remains stationary and, therefore, does not operate the shutter trip lever 16. A movable indicator or pointer 24c (see FIG. 2) in combination with the diaphragm setting ring 24 projects outwardly at the periphery of the shutter housing and moves with the diaphragm setting" ring 24 over a diaphragm aperture scale 60 provided at the periphery of the shutter housing. When the diaphragm setting ring arrest position is reached, the pointer 24a indicates a numerical value on the scale 60, which corresponds to the size of the diaphragm aperture at this position. When the finger tab is released, the first and second action bars 32 and 36 return to their starting positions and thereafter the camera trip rod 18 can be operated to obtain a new diaphragm setting followed by tripping of the shutter to effect an exposure.

The combination of this invention of the diode with a logarithmic characteristic curve in series with the photo resistor ensures that the variation in the voltage drop across the resistor corresponds to the logarithm of the current. Consequently, when the intensity of illumination incident on the photo resistor R is doubled, for example, the voltage drop across the diode Z will always vary by a specific and like amount. Consequently, the resistance element of the potentiometer P can be a linear winding, that is, can be a winding that has a linear voltage drop from one end to the other of the element at a constant current flow therethrough. Such a winding can readily and economically be made with the requisite accuracy.

A feature of advantage of the resistors R1 and R2 in the specific embodiment illustrated, which are associated with the potentiometer P and which can be set during assembly, is that various other characteristics of the photo resistor R can be compensated for. With these resistors being temperature sensitive, the effect of temperature changes on the performances of the photo resistor R and the diode Z can be offset readily.

Still another feature of advantage in the specific embodiment illustrated is that because the photo resistor is constantly illuminated by scene light during the diaphragm setting operation, disturbing inertia effects are inhibited.

It should be noted that the electromechanical arrangement of this invention can also be used for setting other exposure controls, such as shutter speed or time instead of diaphragm aperture, or for setting both speed and aperture, as for example in a so-called programmed shutter. Moreover, concepts of this invention are applicable to other types of electronic circuits for photographic apparatus, for example, to a bridge circuit with a servosystem for setting the diaphragm aperture.

It is seen from the foregoing disclosure that the objects and purposes of the invention are well fulfilled. It is to be understood that the disclosure is given by way of illustrative example only, rather than by way of limitation, and that without departing from the invention, the

details may be varied within the scope of the appended claims.

What is claimed is:

1. A photographic camera comprising an adjustable diaphragm having a rotatable diaphragm setting ring normally at a limit position, means including an electromagnet for controlling the extent to which said ring may rotate from said limit position to an adjusted position, and electric circuit means for controlling said magnet, said circuit means including a photo resistor responsive to light reflected from a scene to be photographed, the resistance of said resistor being a non-linear function of the intensity of light falling thereon, said circuit means also including a diode having an approximately logarithmic characteristic curve deviating from a linear function in a direction opposite to the direction of deviation of said resistor from a linear function.

2. A construction as defined in claim 1, wherein said deviation of said photo resistor in one direction is approximately balanced by said deviation of said diode in the opposite direction, so that said photo resistor and said diode in combination with each other have an approximately linear characteristic.

3. A construction as defined in claim 1, wherein said electric circuit means further includes a potentiometer having a resistance element and a slide member element cooperating with said resistance element, one of said elements being connected to said rotatable ring to be moved relative to the other of said elements by rotation of said ring, said deviation of said photo resistor in one direction being approximately balanced by said deviation of said diode in the opposite direction, so that said photo resistor and said diode in combination with each other have an approximately linear characteristic and may be used in said circuit with said potentiometer having a linear characteristic, without requiring a special potentiometer with a non-linear characteristic.

4. Apparatus according to claim 1, wherein said circuit means comprise a bridge circuit with one branch of said circuit containing said photo resistor and said diode and the other branch of said circuit comprising said resistance element of said potentiometer, said potentiometer having a slide member in electrical combination with circuit means for sensing when said slide member is at the electrical balance point of said bridge.

5. Apparatus according to claim 4, wherein said circuit for sensing when said slide member is at the electrical balance point of said bridge.

6. Apparatus according to claim 5, wherein said diaphragm setting ring is coupled to said slide member, and said circuit means for sensing when said slide member is at the electrical balance point of said bridge comprise an emitter-coupled Schmitt trigger circuit.

7. Photographic apparatus according to claim 6, Wherein said resistance element of said potentiometer is coupled to a movable exposure time setting ring and is movable with said ring.

8. Photographic apparatus according to claim 6, which comprises an adjustable light restrictor in the path of scene light to said photo resistor for taking into account the film speed factor.

References Cited JAMES W. LAWRENCE, Primary Examiner C. R. CAMPBELL, Assistant Examiner US. Cl. X.R. 

